Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.69   13.625%   $96.229   $96.23   $96.25   $96.20  
  Purchase #2 $213.74   10.373%   $235.9113   $235.91   $235.90   $235.90  
  Purchase #3 $194.48   6.713%   $207.5354   $207.54   $207.55   $207.50  
  Purchase #4 $24.30   6.853%   $25.9653   $25.97   $25.95   $26.00  
  Purchase #5 $114.62   13.786%   $130.4215   $130.42   $130.40   $130.40  
  Purchase #6 $170.78   7.746%   $184.0086   $184.01   $184.00   $184.00  
  Purchase #7 $125.46   10.577%   $138.7299   $138.73   $138.75   $138.70  
  7 purchase totals = $928.07       $1,018.8010   $1,018.81   $1,018.80   $1,018.70